One example of a gas discharge lamp is neon tubing, which is often used in signage. Although the following discussion will refer to transformers used for neon tubing or signs, it will be understood that principles of the present invention have application to transformers for other gas discharge tube lamps as well. Power supplies for neon signs use a transformer to convert a low impedance, low voltage power source, for example, a known 60 Hz AC line power having a line voltage in a range of about 100-250 Volts (“VAC”), to a higher voltage source, for example, 15 KiloVolts, suitable for illuminating the neon sign. The 120 Volt AC line power is connected to a low voltage primary winding of the transformer and the high voltage secondary winding of the transformer is connected to the neon sign.
A known gas discharge lamp power supply 20 is shown in FIGS. 12 and 13. The power supply 20 has a baseplate 22, a pair of opposed side walls 24, 26 and a pair of end walls 28, 30. The side walls 24, 26 are substantially perpendicular to the end walls 28 and 30 and all of the walls 24-30 are substantially perpendicular to the baseplate 22. A cover 32 is fastened over the walls 24-30 to form a housing or enclosure 34. Input terminals 36, 38 are provided for connecting respectively a black wire and a white wire of a line voltage source, for example, 120 VAC. A ground terminal 40 is provided for connecting to a ground wire of the line voltage source and is connected to an equipment ground, that is, a green wire ground, within the power supply 20.
A gas discharge lamp, for example, neon tubing, is connected to the high voltage output terminals 42, 44. The power supply 20 is often placed at locations that are not immediately adjacent to the neon tubing and often are not easily accessible. For example, the power supply 20 may be placed in an attic area of a building adjacent a wall supporting a neon sign. In other applications, the power supply 20 may be dropped into an electrical raceway that is accessible only from a top side. If the power supply 20 is placed in a raceway, only the cover 32 is easily seen. The terminals 36-44 and switch 46 extend from generally vertical end walls 28, 30 and are difficult to access. Further, the LED 48 also being on a vertical end wall is difficult to see and may require some determination on the part of a service person to view. Thus, the gas discharge lamp power supply 20, when placed in an electrical raceway, that itself may not be readily accessible, presents various challenges to service personnel in attempting to troubleshoot and repair the power supply.
A concern with known neon sign power supplies is that a potentially dangerous ground fault current may occur anytime there is a relatively low impedance path from one of the high voltage output leads of the neon power supply to ground. Such a path may be formed if a neon sign is carelessly installed so that one of the output leads connected to the sign is in contact with a low impedance in a window frame, doorway, or other ground-connected relatively low impedance. To detect ground fault current, a ground fault detection circuit is connected to the secondary winding of the power supply transformer; and if a secondary ground fault is detected, power to the transformer circuit is automatically interrupted.
Other concerns with known neon sign power supplies are that an installer or service person may inadvertently reverse the line power connections to the low voltage input terminals of the power supply, or an equipment ground may be improperly connected. In other situations, an installer may connect a neon sign power supply that is rated for a lower voltage, for example, 120 VAC to a higher line voltage, for example, 277 VAC. In this example, the power supply will function normally for some period of time but will then fail.
As previously noted, troubleshooting a neon sign for ground faults and other problems is difficult because often the power supply may be located in a building attic area or an electrical raceway, which makes the power supply hard to view and access. Further, in such a location, improper and/or poor connections and ground faults are rarely visibly detectable and servicing the power supply is difficult. Known gas discharge lamp power supplies enable an installer or field engineer to identify and pinpoint the location of a ground fault quickly and accurately, thereby speeding installation and minimizing the temptation for tampering with the ground fault detection circuitry. Various neon sign power supplies, circuits connectable thereto and methods for diagnosing faults are known and described in U.S. Pat. Nos. 6,366,208; 6,040,778 and 5,847,909, which patents are hereby incorporated in their entirety by reference herein.
It is known in a neon sign power supply to create error codes that identify respective fault conditions and communicate those error codes to an installer or service person by illuminating one or more visual indicators, for example, the gas discharge lamp, other lights, LEDs, etc. Further, an error code remains stored and the visual indicator remains illuminated for as long as line power is supplied to the power supply. However, upon approaching a power supply with a reported malfunction, experience, intuition and training cause a service person to first remove line power prior to any handling, visual inspection or other service activity. However, upon removing the line power, the error code stored in the power supply is lost and the visual indicator is turned off. Therefore, the value of the power supply's self diagnostic capability of generating and displaying an error code is lost. Further, upon the service person restoring line power, if the fault condition is intermittent, the error code will not reappear; and the fault identifying visual indicator will not relight. Again, the usefulness of the power supply's self diagnostic capability is lost. Without any guidance as to the source of the problem, especially an intermittent one, the neon sign can experience extended periods of no illumination and downtime.
Thus, there is a need for an improved neon sign power supply that eliminates the disadvantages of known power supplies as discussed above.